Photographic and cinematographic objective of large focal length



Nov. 24, 1959 R. SOLISCH 2,913,955

PHOTOGRAPHIC AND CINEMATOGRAPHIC OBJECTIVE on LARGE FOCAL LENGTH FiledFeb. 21, 1958 2 a 34 x 2 a #5 INVENTOR: P012041: Sausw United StatesPatent PHOTOGRAPHIC AND CINEMATOGRAPHIC 0B- JECTIVE OF LARGE FOCALLENGTH Rudolf Solisch, Gottingen, Germany, assignor to Isco OptischeWerke G.m.b.H., Gottingen-Weende, Germany Application February 21, 1958,Serial No. 716,716 Claims priority, application Germany March 15, 1957 6Claims. (Cl. 88-57) My present invention relates to optical objectivesof large focal length designed for photographic or cinematographiccameras.

A known type of objective of large focal length comprises a group ofthree components positioned forwardly of a diaphragm space, i.e. on theobject side of the system, and a single component behind this space,i.e. on the image side. The general object of my invention is to providean improved system of this type in which the back-focal distance issmall, preferably less than onethird of the overall focal length, andwhich can be designed for relative apertures up to 1:4 or even 1:2.8without objectionable distortion. A more particular ob ject of theinvention is to provide an objective system of this character whoseimage-side portion is of reduced dimensions to facilitate installationin certain types of camera.

According to a feature of my invention there is provided an objectivesystem of the general type referred to whose three object-sidecomponents, the first two of which are advantageously in the form ofpositive menisci facing with their convex sides away from the diaphragmspace and the third of which preferably consists of two cemented orair-spaced members of opposite refractivity, are so dimensioned that theaxial thickness of the foremost component exceeds 12% of the overallfocal length of the system and that the combined axial thickness of theother two front components (including their intervening air space orspaces) exceeds 25% of this overall focal length.

Other features of my improved system, designed to afiord maximumcorrection of aberrations, are the provision of a single positive lensof axial thickness greater than of the overall focal length as theimage-side component and a design of all the components in such mannerthat the total physical length of the system, measured from the rearvertex of the sole back component to the forward vertex of the foremostfront component, exceeds 200% of the back-focal distance measuredbetween the aforesaid rear vertex and the image plane. Another featuredesirable from the viewpoint of stressing aberrations is a relativedimensioning of the radii of adjacent surfaces of the second and thirdfront components in such manner that the air space defined thereby hasthe shape of a negative meniscus.

A further feature of the invention, designed to reduce the manufacturingcost of my improved objectives, resides in the selection of glasses forthe first front component and for the forward (positive) lens element ofthe third front component having an index of refraction less than 1.59for the yellow helium line of the spectrum, it be- Patented Nov. 24,1959 ing at the same time desirable to give the rear (negative) lenselement of the third component an index of refraction exceeding by 0.12that of its positive mate.

The invention will be further described with reference to theaccompanying drawing in which Figs. 1 and 2 represent two embodiments.In Fig. 1 I have shown an optical objective with three front componentsI, II, III and one rear component IV separated by a diaphragm space.Component I is a positive meniscus L having radii r r and thickness dcomponent II, separated from component I by an air space d is a similarmeniscus L having radii r r, and thickness d A further air space dhaving the shape of a negative meniscus, separates component II fromcomponent III which is a dispersive, meniscus-shaped doublet composed ofa biconvex lens L (radii r r and thickness d and a biconcave lens L(radii r r and thickness d Beyond the diaphragm space 11-; there isprovided the single rear component IV in the form of a positive meniscusL having radii r r and thickness d With an overall focal length ofnumerical value 100, a back-focal distance s'=30.08 and an apertureratio up to 1:28, the radii r; to r and the thicknesses and separationsd to d of lenses L to L as well as their refrac- In Fig. 2 I have showna modified system comprising a front portion consisting of the threecomponents I, II, III and a rear portion represented by the single rearcomponent IV'; components I, II and IV are single lenses L (radii r r,and thickness d;'), L, (radii r r, and thickness d and L (radii r r andthickness d similar to the corresponding lenses L L L in Fig. 1.Component III differs from its counterpart in Fig. 1 by the fact thatits biconvex lens element L (radii r r and thickness d and its biconcavelens element L (radii r r and thickness d,) are no longer cementedtogether but are separated by an air space d having the shape of apositive meniscus, the convex side of this meniscus being turned towardthe diaphragm space d The air spaces separating lens L, from lenses IIand L have been designated d, and d respective y.

With the assumption of a numerical value for the overall focal length ofthe system of Fig. 2, the same may have a back-focal distance s'=29.93and an aperture ratio up to 1:28. The radii r to r and the thicknessesand separations a to d, of its lenses L to L as well as their refractiveindices n and their Abb numbers 7 may have numerical valuessubstantially as given in the following table:

An examination of both the foregoing tables shows that in each instancethe axial thickness of the first front component L or L lies between thenumerical values 30 12 and 16.5, that the sum of thicknesses d;, to d ord to d, of the second and third components ranges between numericalvalues 25 and 33, and that the thickness d or d,;' of the rear componentL or L is between numerical values 10 and 13.5. Also, the indices ofrefraction ri of lenses L L and L L for the yellow helium line are lessthan 1.59 whereas the refractive indices of lenses L L exceed those oflenses L L by more than 0.12. The total physical length d d' is in eachcase more than double but less than triple its back-focal distance s, s.

Within the operative limits given hereinabove and in the appendedclaims, the parameters of an objective system of the general characterset forth may be modified without departing from the spirit and scope ofthe invention.

I claim:

1. An optical objective system with a back-focal distance less thanone-third its overall focal length, comprising a three-component frontportion consisting of a positive first component, a positive secondcomponent and a negative third component; and a rear portion separatedfrom said front portion by a dia hragm space, said rear portionconsisting of a positive foui'ffi component; the axial thickness of saidfirst component be ing greater than 12% but less than 16.5% of saidoverall focal length, the total thickness of said second and thirdcomponents being greater than but less than 33% of said overall focallength, said third component being composed of a positive and a negativelens element, the axial thickness of said fourth component exceeding 10%but being less than 13.5% of said overall focal length, said first andsecond components consisting each of a meniscus-shaped lens elementturning its convexity away from said diaphragm space, the combined axiallength of said portions and of said diaphragm space being greater thantwice but less than three times said back-focal distance, said secondand third components enclosing a distinctly negative-meniscus-shaped airspace.

2. An optical system according to claim 1 wherein said negative lenselement is a biconcave lens and said positive lens element is a biconvexlens.

3. An optical system according to claim 2 wherein said biconcave lens iscemented onto and follows said biconvex lens.

4. An optical system according to claim 3 wherein said first, second andfourth components are single lenses L L and L respectively, and whereinthe radii r to r,, the thicknesses and separations d to d the refractiveindices 71,, and the Abb numbers v of said lenses L L L said biconvexlens L and said biconvex lens L have numerical values, based upon anoverall focal length of numerical value 100, substantially as given inthe following table:

5. An optical system according to claim 2 wherein said biconcave lensfollows said biconvex lens ,andmis.

separa, e t ere rorn y an air space in the shape of a 0 a "positivemeniscus.

6. An optical system according to claim 5 wherein said first, second andfourth components are single lenses L L and L respectively, and whereinthe radii r to r the thicknesses and separations d, to 11,, therefractive indices n and the Abb numbers w of said lenses L L L saidbiconvex lens 1., and said biconvex lens 1., have numerical values,based upon an overall focal length of numerical value 100, substantiallyas given in the following table:

n=+ 57.28 L1 d1'=14.s9 1.5582 67.8

d1'= 0.08 air space r3'=+ 36.24 L1 d;'- 8.40 1.6031 60.7

d,- 0.15 air space r;'=+ 59.81 L, d;= 9.78 1. 5673 42.8

(10 0.08 air space T7'=133.05 L. d1=10.85 1. 7215 29.3

d '=17.57 air (diap space r,'=+ 64.49 L, iv-11.40 I 1.6990 30.1

References Cited in the file of this patent UNITED STATES PATENTS1,584,272 Bertele May 11, 1926 1,998,704 Bertele Apr. 23, 1935 2,105,799Tronnier Jan. 18, 1938 2,141,733 Bertele Dec. 27, 1938 2,481,688 Schadeet a1. Sept. 13, 1949 2,543,856 Kupka Mar. 6, 1951 2,622,479 BerteleDec. 23, 1952 FOREIGN PATENTS 350,323 Great Britain June 11, 1931

